Antenna arrays are widely used in many military as well as civil applications. They are typically expensive to develop and the design cycles are long. Unfortunately, due to the vastly different personalities required for various applications, the technology developed for one project cannot be easily adapted to another one, causing a lot of waste in terms of time, effort, and money. Traditionally, antenna arrays are custom-designed for certain applications. This is mainly due to two reasons. First, there are numerous electrical parameters that need to be designed to address a specific application. In order to meet all the requirements, the optimized antenna physical structures are very different among diverse applications. As a result, the commonality between different antenna systems is rare. Second, the lack of good tuning mechanisms prevents antennas from being reconfigured to satisfy different personalities.
In the last decade, due to the popularity of the Cognitive Radio (CR) concept, a lot of developments in tunable antenna and radio frequency (RF) front-ends have been seen. These tunable antennas are often preferred over the traditional ultra-wideband approach because the tunable antenna can be designed to achieve a relatively narrower bandwidth, therefore, effectively rejecting the interference from other users and reducing unwanted noise. In theory, reconfigurable antennas should exhibit the ability to change many RF communication parameters, such as carrier frequency, bandwidth, polarization, radiation pattern, power level etc. However, current techniques are only capable of modifying one or two of these aforementioned parameters. Frequency tunability has been demonstrated using photoconductive switches, varactor diodes, integrated filtenna, PIN diodes, both varactors and PIN diodes, or mechanical rotors. Antennas with reconfigurable bandwidth, polarization, radiation main beam and radiation null have also been reported. Switchable carrier frequency and limited reconfigurable radiation patterns have been described. Both frequency and polarization reconfigurable antenna have been demonstrated. Albeit useful, the aforementioned technologies cannot be directly applied to antenna arrays, particularly due to the lack of the necessary agility required to provide digitally-interconnected building blocks from which larger systems can be formed.
In response to the need for reconfigurable antenna arrays which can adapt to different personalities, a pixel patch antenna has been designed using micro-actuators. Nevertheless, the frequency tuning range is rather limited. A similar technique, Pixel Addressable Reconfigurable Conformal Antenna (PARCA), in which the antenna substrate is divided into many pixels is known in the art. Under each pixel there is a mechanical actuator. By selectively raising or lowering each pixel, antennas of different sizes (which determines the frequency) and other parameters can be realized. While the technique has the advantage of high power-handling capabilities and high linearity, there are drawbacks associated with the technology. A large number of mechanical actuators are required, therefore increasing the cost and weight of the antenna system. The tuning speed is slow (on the order of milliseconds at the best). In addition, the lateral metal connection is achieved by mere mechanical contact, which could lead to reliability issues since good conductivity within the antenna surface is mandated. The limited choice of antenna type and feeding network (primarily patch antenna and inset microstrip feeding) is not sufficient to satisfy different personalities which require more than just frequency tuning. One alternative approach is to use switches to connect the pixelated patch antennas. For this configuration, the pixelated patch antenna elements are not moved up and down, but are instead connected laterally through a mesh of switches such as MEMS (Micro-Electromechanical Systems). By turning these switches ON and OFF, one can dynamically change the frequency, polarization, and bandwidth (possibly through the matching network). However, the large quantities of electronic switches required for this implementation will require a very expensive voltage controller in order to set the bias voltage for each switch. Moreover, when this pixelated antenna is reconfigured into an array, the mutual coupling between antenna elements could be large enough to cause scan blindness due to the closely-spaced pixelated elements, even when the switches are off. Similar to the mechanical actuator approach, the feeding of this antenna array is also very challenging to realize to satisfy the requirements for different personalities.
Accordingly, what is needed in the art is an improved reconfigurable antenna array that is adaptable to different personalities of communication, such as radar and electronic warfare (EW) systems.